Significant research into the phenomena of oxidation within matrix beds of heat resistant materials that are contained within a thermal oxidizer has recently been undertaken. Because such oxidation can occur outside the normal premixed fuel/air flammability limits, the technology can be called "flameless." In this regard U.S. Pat. Nos. 4,688,495 (Galloway) and 4,823,711 (Kroneberger et al.) disclose early work on matrix oxidation technology. In addition, U.S. Pat. Nos. 5,165,884 (Martin et al.) and 5,320,518 (Stilger et al.), and application Ser. No. 08/393,023 (Holst et al.), filed Feb. 23, 1995 now U.S. Pat. No. 5,533,890,discuss in significant detail the technology involved in the designing of thermal oxidizers. The issued Martin et al., Holst et al., Stilger et al., Galloway, and Kroneberger et al. patents are hereby incorporated in their entireties by reference.
The thermal oxidizers set forth in the Martin et al. patent generally contained a matrix bed of solid, heat resistant material. Such thermal oxidizers functioned to destroy VOCs within a process gas stream by passing those gases through the matrix bed, which was heated to a temperature above the autoignition point of the process gases. The thermal oxidizers set, forth in Martin et al. can be referred to as "straight-through" units in that the flow path of the process gases through the matrix bed is direct, with the gases entering at either the bottom or top and exiting at the opposite end, thus passing straight through the matrix bed.
Previously, the straight-through thermal oxidizers have been preheated generally by directing heated gases through the matrix bed in the same flow path as that taken by the process gases. Such preheating systems and methods for preheating of the matrix bed are discussed in the Martin et al. patent. Typically, the preheating procedure was conducted until the entire matrix bed was heated to a temperature above the autoignition point of the process gases, commonly above about 1400.degree. F.
The preheating procedure was a relatively time-consuming process due to the fact that the matrix materials efficiently absorbed the heat from the preheating gases. In such a way, the temperature of the matrix bed was generally not raised in a uniform fashion, but rather the portion of the matrix bed proximate to the preheating gas inlet was initially heated to high temperatures and thereafter the temperature of the rest of the matrix bed was gradually raised in a "thermal wave-like" fashion.
After the matrix bed was heated, cooling gases, typically air, were directed into the oxidizer to cool the plenum area and the lower portion of the matrix bed to a temperature below the autoignition temperature. This cooling step was conducted to avoid any safety hazards associated with the unwanted oxidation of the process gases prior to their entering into the matrix bed.
A need therefore exists to optimize the preheating process associated with straight-through thermal oxidizers. Efficiencies in operating time and costs could be obtained if processes could be developed to decrease the time to preheat the matrix bed and to avoid altogether the need to cool the preheated bed.